- ID:
- ivo://CDS.VizieR/J/ApJ/895/52
- Title:
- EW and chemical abundances in 211 stars with HARPS
- Short Name:
- J/ApJ/895/52
- Date:
- 15 Mar 2022 07:30:10
- Publisher:
- CDS
- Description:
- Magnetic fields and stellar spots can alter the equivalent widths of absorption lines in stellar spectra, varying during the activity cycle. This also influences the information that we derive through spectroscopic analysis. In this study, we analyze high-resolution spectra of 211 sunlike stars observed at different phases of their activity cycles, in order to investigate how stellar activity affects the spectroscopic determination of stellar parameters and chemical abundances. We observe that the equivalent widths of lines can increase as a function of the activity index log R_HK_' during the stellar cycle, which also produces an artificial growth of the stellar microturbulence and a decrease in effective temperature and metallicity. This effect is visible for stars with activity indexes log R_HK_'>=-5.0 (i.e., younger than 4-5Gyr), and it is more significant at higher activity levels. These results have fundamental implications on several topics in astrophysics that are discussed in the paper, including stellar nucleosynthesis, chemical tagging, the study of Galactic chemical evolution, chemically anomalous stars, the structure of the Milky Way disk, stellar formation rates, photoevaporation of circumstellar disks, and planet hunting.
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Search Results
- ID:
- ivo://CDS.VizieR/J/A+A/635/A114
- Title:
- EW and [Fe/H] for 30000 globular cluster RGB stars
- Short Name:
- J/A+A/635/A114
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The CaII triplet in the near-infrared at 8498, 8542, and 8662{AA} is visible in stars with spectral types between F and M and can be used to determine their metallicities. We calibrated the relation using average cluster metallicities from literature and MUSE spectra, and extend it below the horizontal branch - a cutoff that has traditionally been made to avoid a non-linear relation - using a quadratic function. In addition to the classic relation based on V-\vhb$ we used calibrations based on absolute magnitude and luminosity and used it for those cluster, for which no HB brightness was available. The obtained relations are then used to calculate metallicities for all the stars in the sample.
- ID:
- ivo://CDS.VizieR/J/ApJ/786/74
- Title:
- EW measurements of 6 Segue 1 red giants
- Short Name:
- J/ApJ/786/74
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present Magellan/MIKE and Keck/HIRES high-resolution spectra of six red giant stars in the dwarf galaxy Segue 1. Including one additional Segue 1 star observed by Norris et al. (2010ApJ...722L.104N), high-resolution spectra have now been obtained for every red giant in Segue 1. Remarkably, three of these seven stars have metallicities below [Fe/H]=-3.5, suggesting that Segue 1 is the least chemically evolved galaxy known. We confirm previous medium-resolution analyses demonstrating that Segue 1 stars span a metallicity range of more than 2 dex, from [Fe/H]=-1.4 to [Fe/H]=-3.8. All of the Segue 1 stars are {alpha}-enhanced, with [{alpha}/Fe]~0.5. High {alpha}-element abundances are typical for metal-poor stars, but in every previously studied galaxy [{alpha}/Fe] declines for more metal-rich stars, which is typically interpreted as iron enrichment from supernova Ia. The absence of this signature in Segue 1 indicates that it was enriched exclusively by massive stars. Other light element abundance ratios in Segue 1, including carbon enhancement in the three most metal-poor stars, closely resemble those of metal-poor halo stars. Finally, we classify the most metal-rich star as a CH star given its large overabundances of carbon and s-process elements. The other six stars show remarkably low neutron-capture element abundances of [Sr/H]<-4.9 and [Ba/H]<-4.2, which are comparable to the lowest levels ever detected in halo stars. This suggests minimal neutron-capture enrichment, perhaps limited to a single r-process or weak s-process synthesizing event. Altogether, the chemical abundances of Segue 1 indicate no substantial chemical evolution, supporting the idea that it may be a surviving first galaxy that experienced only one burst of star formation.
- ID:
- ivo://CDS.VizieR/J/A+A/633/A38
- Title:
- EW of 10 solar-type stars of Praesepe
- Short Name:
- J/A+A/633/A38
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Open clusters exquisitely track the Galactic disc chemical properties and its time evolution; a substantial number of studies and large spectroscopic surveys focus mostly on the chemical content of relatively old clusters (age>1Gyr). Interestingly, the less studied young counterpart populating the solar surrounding has been found to be solar (at most), with a notable surprising lack of young metal-rich objects. While there is wide consensus about the moderately above-solar composition of the Hyades cluster, the metallicity of Praesepe is still controversial. Recent studies suggest that these two clusters share identical chemical composition and age, but this conclusion is disputed. With the aim of reassessing the metallicity of Praesepe, and its difference (if any) with the Hyades cluster, we present in this paper a spectroscopic investigation of ten solar-type dwarf members. We exploited GIARPS at the TNG to acquire high-resolution, high-quality optical and near-IR spectra and derived stellar parameters, metallicity ([Fe/H]), light elements, alpha- and iron-peak elements, by using a strictly differential (line-by-line) approach. We also analysed in the very same way the solar spectrum and the Hyades solar analogue HD 28099. Our findings suggest that Praesepe is more metal-rich than the Hyades, at the level of [Fe/H]=+0.05+/-0.01dex, with a mean value of [Fe/H]=+0.21+/-0.01dex. All the other elements scale with iron, as expected. This result seems to reject the hypothesis of a common origin for these two open clusters. Most importantly, Praesepe is currently the most metal-rich, young open cluster living in the solar neighbourhood
- ID:
- ivo://CDS.VizieR/J/A+A/527/A18
- Title:
- EW of 6 subgiants of {omega} Cen
- Short Name:
- J/A+A/527/A18
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We analysed high-resolution UVES spectra of six stars belonging to the subgiant branch of {omega} Centauri, and derived abundance ratios of 19 chemical elements (namely Al, Ba, C, Ca, Co, Cr, Cu, Fe, La, Mg, Mn, N, Na, Ni, Sc, Si, Sr, Ti, and Y). A comparison with previous abundance determinations for red giants provided remarkable agreement and allowed us to identify the sub-populations to which our targets belong. We found that three targets belong to a low-metallicity population at [Fe/H]=-2.0dex, [alpha/Fe]=+0.4dex and [s/Fe]=0dex. Stars with similar characteristics were found in small amounts by past surveys of red giants. We discuss the possibility that they belong to a separate sub-population that we name VMP (very metal-poor, at most 5% of the total cluster population), which - in the self-enrichment hypothesis - is the best-candidate first stellar generation in {omega} Cen. Two of the remaining targets belong to the dominant metal-poor population (MP) at [Fe/H]=-1.7dex, and the last one to the metal-intermediate (MInt) one at [Fe/H]=-1.2dex. The existence of the newly defined VMP population could help to understand some puzzling results based on low-resolution spectroscopy (Sollima et al. 2005ApJ...634..332S , Villanova et al., 2007, Cat. J/ApJ/663/296) in their age differences determinations, because the metallicity resolution of these studies was probably not enough to detect the VMP population. The VMP could also correspond to some of the additional substructures of the subgiant-branch region found in the latest HST photometry (Bellini et al., 2010, Cat. J/AJ/140/631). After trying to correlate chemical abundances with substructures in the subgiant branch of {omega} Cen, we found that the age difference between the VMP and MP populations should be small (0+/-2Gyr), while the difference between the MP and MInt populations could be slightly larger (2+/-2Gyr).
- ID:
- ivo://CDS.VizieR/J/A+A/502/267
- Title:
- EWs of 31 giant stars of 10 open clusters
- Short Name:
- J/A+A/502/267
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Equivalent widths (EWs) of a sample of 31 giant stars of 10 open clusters. The list includes lines of NaI, MgI, SiI, CaI, ScII, TiI, VI, VII, CrI, CrII, FeI, FeII, CoI, NiI, YII, CeII, and EuII. For most of the lines, EWs were measured using PeakFit. For some Fe II lines, EWs were measured by fitting Gaussian profiles to the lines with the IRAF task SPLOT. The adopted oscillator strengths (loggfs) and excitation potentials (EP) are also listed. For the stars of the clusters NGC 2360 and NGC 2447 only the FeII EWs are given. The EWs of the remaining lines can be found in Hamdani et al. (2000, Cat. J/A+A/360/509).
- ID:
- ivo://CDS.VizieR/J/MNRAS/449/761
- Title:
- EWs of metal-poor stars in the UMi I dSph galaxy
- Short Name:
- J/MNRAS/449/761
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present detailed chemical element abundance ratios of 17 elements with eight<=Z<=60 in three metal-poor stars in the Ursa Minor dwarf spheroidal galaxy, which we combine with extant data from the literature to assess the predictions of a novel suite of galaxy chemical evolution models. The spectroscopic data were obtained with the Keck/High-Resolution Echelle Spectrograph instrument and revealed low metallicities of [Fe/H]=-2.12, -2.13 and -2.67 dex. While the most metal-poor star in our sample shows an overabundance of [Mn/Fe] and other Fe-peak elements, our overall findings are in agreement with previous studies of this galaxy: elevated values of the [{alpha}/Fe] ratios that are similar to, or only slightly lower than, the halo values but with SN Ia enrichment at very low metallicity, as well as an enhancement of the ratio of first to second peak neutron capture elements [Y/Ba] with decreasing metallicity. The chemical evolution models which were tailored to reproduce the metallicity distribution function of the dwarf spheroidal, indicate that Ursa Minor had an extended star formation which lasted nearly 5 Gyr with low efficiency and are able to explain the [Y/Ba] enhancement at low metallicity for the first time. In particular, we show that the present-day lack of gas is probably due to continuous loss of gas from the system, which we model as winds.
- ID:
- ivo://CDS.VizieR/J/A+A/512/A13
- Title:
- EW-Teff calibration for solar-type stars
- Short Name:
- J/A+A/512/A13
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The precise determination of the stellar effective temperature of solar type stars is of extreme importance for Astrophysics. We present an effective temperature calibration for FGK dwarf stars using line equivalent width ratios of spectral absorption lines. The ratios of spectral line equivalent width can be very sensitive to effective temperature variations for a well chosen combination of lines. We use the automatic code ARES to measure the equivalent width of several spectral lines, and use these to calibrate with the precise effective temperature derived from spectroscopy presented in a previous work.
- ID:
- ivo://CDS.VizieR/J/ApJ/847/38
- Title:
- Extreme emission line galaxies at z<~0.05
- Short Name:
- J/ApJ/847/38
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Searching for extreme emission line galaxies allows us to find low-mass metal-poor galaxies that are good analogs of high redshift Ly{alpha} emitting galaxies. These low-mass extreme emission line galaxies are also potential Lyman-continuum leakers. Finding them at very low redshifts (z<~0.05) allows us to be sensitive to even lower stellar masses and metallicities. We report on a sample of extreme emission line galaxies at z<~0.05 (blueberry galaxies). We selected them from SDSS broadband images on the basis of their broadband colors and studied their properties with MMT spectroscopy. From the entire SDSS DR12 photometric catalog, we found 51 photometric candidates. We spectroscopically confirm 40 as blueberry galaxies. These blueberries are dwarf starburst galaxies with very small sizes (<1kpc) and very high ionization ([OIII]/[OII]~10-60). They also have some of the lowest stellar masses (log(M/M_{sun}_)~6.5-7.5) and lowest metallicities (7.1<12+log(O/H)<7.8) of starburst galaxies. Thus, they are small counterparts to green pea galaxies and high redshift Ly{alpha} emitting galaxies.
- ID:
- ivo://CDS.VizieR/J/ApJ/742/111
- Title:
- Extreme emission-line galaxies in CANDELS
- Short Name:
- J/ApJ/742/111
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We identify an abundant population of extreme emission-line galaxies (EELGs) at redshift z~1.7 in the Cosmic Assembly Near-IR Deep Extragalactic Legacy Survey imaging from Hubble Space Telescope/Wide Field Camera 3 (HST/WFC3). Sixty-nine EELG candidates are selected by the large contribution of exceptionally bright emission lines to their near-infrared broadband magnitudes. Supported by spectroscopic confirmation of strong [OIII] emission lines - with rest-frame equivalent widths ~1000{AA} - in the four candidates that have HST/WFC3 grism observations, we conclude that these objects are galaxies with ~10^8^M_{sun}_ in stellar mass, undergoing an enormous starburst phase with M_*_/(dM/dt)_*_ of only ~15Myr. These bursts may cause outflows that are strong enough to produce cored dark matter profiles in low-mass galaxies. The individual star formation rates and the comoving number density (3.7x10^-4^Mpc^-3^) can produce in ~4Gyr much of the stellar mass density that is presently contained in 10^8^-10^9^M_{sun}_ dwarf galaxies. Therefore, our observations provide a strong indication that many or even most of the stars in present-day dwarf galaxies formed in strong, short-lived bursts, mostly at z>1.
